In communication devices, radar devices, or the like, a power amplifier that amplifies the power of a transmission signal up to a desired level is mounted. In such a power amplifier, a semiconductor element such as a High Electron Mobility Transistor (HEMT) or a Field Effect Transistor (FET) is used.
The self-heating of a semiconductor element increases with increase in the power of a power amplifier. In order to reduce the performance degradation which is caused by the self-heating of a semiconductor element, an improvement in the efficiency is required in the power amplifier. As a method for improving the efficiency of the power amplifier, conventionally, a higher harmonic processing circuit is attached to a power amplifier, as shown in Patent Literature 1, for example. In this power amplifier, by disposing a higher harmonic processing circuit on an input side, the impedance for a second harmonic wave appearing at the gate terminal of a semiconductor element is short-circuited, and as a result, the voltage of a second harmonic wave appearing between the drain and the source of the semiconductor element is reduced to 0. As a result, the power loss in the higher harmonic wave is suppressed, and an improvement in the efficiency of the power amplifier is achieved.